The present invention relates to electronic keyboard-operated musical instruments in general, and more particularly to improvements in digital control circuit arrangements which can be used in electronic organs or analogous musical instruments and utilize a sampling circuit which generates a series of pulses denoting the actuated keys of a keyboard, a data signal generator with a time delay for transmission of data signals in dependency on the aforementioned series of pulses and a tone evaluating circuit which receives the data signals.
U.S. Pat. No. 3,697,661 granted Oct. 10, 1972 to Deutsch discloses a multiplexed pitch generator system for use in a keyboard-operated musical instrument wherein a shift register is utilized to delay the entire key signal, namely, the signal which denotes the actuated or depressed keys of the keyboard. In other words, the melody played by the operator of the keyboard has a footage or rank different from that which is associated with the notes corresponding to the actuated keys. The patented system further employs a summing circuit which is connectable with the input of the shift register on closing of a first switch and which is also connectable with various stages of the shift register on closing of additional switches. This means that actuation of a single key can effect the generation of several pitches. An advantage of the patented system is that the means for transmitting signals to the tone evaluating circuit comprises a small number of conductors. In fact, it is possible to operate with a single conductor. Reference may be had to pages 53-56 of the article by A. W. Critchley entitled "Multiplex keying system for organs" published in the January 1981 issue of "Wireless World."
German Auslegeschrift No. 23 62 609 discloses a circuit for transporting the pitch in an electronic keyboard-operated musical instrument wherein the transposing means employs shift registers.
A system known as Siemens SMT employs a control circuit without the possibility of delaying the key signals. The data signal which is generated by this system has sixtyfive time slots of which sixtyone are designed for a maximum of sixtyone keys (five octaves with twelve notes each and the highest C). The slots sixtytwo to sixtyfive are designed for four information pulses which denote, for example, the footages to be processed as well as the various types of sustain. The pulse frequency is in the range of 40 to 60 kilohertz. The sampling cycle invariably begins at the highest key of the keyboard. In the tone evaluating circuit, the pulses of the key signal are used directly to switching-through impulses so as to generate a tone which corresponds to the actuated key by taking into consideration the selected footage. The same system can be employed if the keyboard consists of fortynine keys (four octaves of twelve notes each and an upper C). The time slots one to twelve or fifty to sixtyone remain free as a result of shortening of the tone signal.